The present invention relates generally to disc drives. More particularly, the present invention relates to an improved disc clamp for use in securing a disc stack.
In disc drives, data is recorded on and read from one or both surfaces of a disc. To increase storage capacity, more than one disc may be used. Data is stored in addressable units called sectors which are arranged in generally circular tracks defined on the disc surface. In operation, a read/write device, referred to as a head, is held over (or under, as the case may be) the appropriate track and the disc is rotated so that the head reads from or writes to a series of sectors along the same track. The head is supported by an actuator that is used for changing the position of the head relative to the tracks. The discs are thus mounted to the hub of a spindle motor for the required rotational motion, and are vertically spaced apart to allow for access by the heads. Typically, discs are alternately stacked with spacers on the spindle hub forming a disc stack that is secured to the spindle hub by a disc clamp. Slippage of the discs can, for example, result in track misregistration and read/write errors. Therefore it is desired of a disc clamp that it is able to keep the disc stack components in alignment even under high speed rotation and in the presence of large external shocks.
One disc clamp currently in use is in the form of a circular plate with three or more screw holes. It is placed over the top most disc of the disc stack and screws are passed through the screw holes to engage corresponding threaded holes on a top surface of the spindle hub. The need to allow for screw holes imposes a limit to how small the disc clamp may be designed, which in turn means that the amount of disc surface that is covered by the disc clamp and not available for data storage cannot be further reduced.
An alternative type of disc clamps is described in the U.S. Pat. No. 5,548,457, issued on Aug. 20, 1996, to Brooks et al. and in the U.S. Pat. No. 5,940,244, issued on Aug. 17, 1999, to Canlas et al. Instead of using screws to produce a clamping force, a shrink-fit ring is used. The disc clamp is expanded by heating prior to being placed onto the spindle hub. When the disc clamp cools, clamping forces are exerted on the disc stack. Shrink-fit disc clamps typically require heating to a high temperature, and this contributes to higher assembly cost. The process appears to be irreversible and thus may not be suitable for re-work.
The present invention provides an improved disc clamp to meet the continuing need for better quality disc drives that can be manufactured at lower cost. Other advantages of the present invention over the prior art will be evident from the following description.
The present invention relates to an improved disc stack system for use in a disc drive, where the disc stack involves a novel disc clamp.
In accordance with one embodiment of the invention, there is provided an annular disc clamp located in a groove of a spindle hub, where the groove is defined by a ledge and a shoulder. The disc clamp is configured to fit between the ledge and a disc resting on the shoulder. The disc clamp is made from a shape memory alloy. The disc clamp is shaped such that, in an austenitic phase, it has a thickness that is greater than a clearance, where the clearance is the distance from the upper surface of the disc to the ledge. In a martensitic phase, the disc clamp has an inner diameter that is greater than the diameter of the ledge and, in an austenitic phase, it has an inner diameter that is less than the diameter of the ledge. Preferably, the disc stack includes an inclined surface configured for mating with an inclined surface of the disc clamp. Preferably, the disc clamp includes a convex portion to provide a line contact with the disc.
In an alternative embodiment, the disc clamp is located between the upper ledge of the spindle hub and the top-most disc of a multiple-disc disc stack.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.